1. Field of the Invention
The present invention relates to an ultraviolet (UV)-curable composition capable of being photopolymerized under atmospheric conditions, thereby forming a transparent resin having excellent properties.
2. Description of the Related Art
Previously, in the production of transparent resins by photopolymerization, vinyl monomers such as methyl acrylate, methyl methacrylate and others have been generally utilized as the monomeric components.
However, use of those vinyl monomers in the production of the transparent resin suffers from some technical problems. For example, the photopolymerization of such vinyl monomers can be disturbed by oxygen which is dissolved in a polymerization composition containing the monomers or in the atmosphere. Thus, it is very difficult to attain the polymerization and curing of the vinyl monomer-containing compositions in the atmosphere. To avoid this problem, the prior art production methods teach the introduction of an inert gas into the polymerization atmosphere, however, this and results in other problems, including increased costs.
In addition to difficulty in carrying out the polymerization thereof, the vinyl monomers suffer from yellowing or yellow discoloration of the resulting resin. For example, in the polymerization using an acrylic composition as a starting material, it is known that the resin produced upon polymerization of the composition can be yellowed over time, and a degree of the yellowing can be increased with lapse of time. The yellowing problem can be solved or diminished, if an additive such as a blueing agent is added to the acrylic composition. However, blueing agents are expensive and their yellowing-diminishing effect cannot be retained in the resulting resin for an extended period of time. With regard to obtaining an excellent durability and its long-term retention, the problem has not yet been solved in the art.